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Watch: NDP Leader Tom Mulcair discusses his opposition to Bill C-51 and what he would do with the legislation if his party forms government.

OTTAWA —Though vehemently against the bill, NDP Leader Tom Mulcair, if in power, would not necessarily scrap the Conservative’s “anti-terror” bill — but he would definitely change it, he said in an interview Sunday.

“We are very concerned with this bill,” Mulcair said on The West Block with Tom Clark. “We’re worried about the scope. And, frankly, we’re worried about the lack of oversight.”

As the bill weaves its way through Parliament, Mulcair said he is first focusing on convincing the government to amend certain parts now.

“First I’m going to … try to get changes through,” he told Clark. “We’re going to push those every step of the way, in every committee hearing and in every different reading in the House.”

Without amendments the NDP will vote against the bill and Mulcair’s office said that’s what separates the NDP from the Liberal Party.

“We have been focused on opposing this bill now, unlike the Liberals who have said they’ll deal with it after the election,” a representative from Mulcair’s office said in an email. “And we have been giving detailed reasons why we’re opposed to this bill because we reject the frame that it’s a done deal.”

Justin Trudeau has said the Liberal Party will vote for the bill, despite concerns it does not include new watchdog powers to guard against abuses.

Trudeau said he will push for amendments to strengthen intelligence oversight and, if that proves unsuccessful, usher in the changes should the Liberals form the next government.

Despite the criticism and opposition to bill C-51, the Conservatives introduced and easily passed a motion last week to impose a time limit on debate before passing the bill to a House of Commons committee.

The bill, tabled late last month in response to the daylight murders of two Canadian soldiers, would give the Canadian Security Intelligence Service more power to thwart suspected terrorist plots.

It would also make it easier for the RCMP to obtain a peace bond to restrict the movements of suspects and extend the amount of time they can be kept in preventative detention.

In addition, it creates a new criminal offence of encouraging someone to carry out a terrorism attack.

The New Democrat argument against the bill is it dangerously overreaches and is too vague — one bit missing from the bill, for example, is a clear definition of what constitutes terrorism, or any definition of “promoting,” “advocating,” or “disrupting.”

“They say that one of the things that they’re allowed to go against is anybody who’s threatening an infrastructure in any way, shape or form,” Mulcair said. “Mr. Harper tried to eviscerate a lot of our environmental legislation to make things easier for some of the big companies to put in [oil] infrastructure, but they’re losing time and again. Is that frustration one of the things that’s driving him here?”

The NDP leader also said the government should focus its efforts on ensuring security agencies have the proper resources to do their jobs.

The NDP is far from alone in their concern about expanding the powers of a Canadian spy agency without strengthening oversight.

WATCH: Former prime minister Joe Clark explains his concern over the government’s new anti-terror bill.

Other critics, including British Columbia-based OpenMedia.ca, have warned some measures in the bill could encourage “reckless” sharing of private information.

The British Columbia Civil Liberties Association, meanwhile, said the bill proposes an “unprecedented expansion of powers” that could harm Canadians while doing little or nothing to protect public safety.

Last week, former prime ministers, Supreme Court justices, privacy commissioners and an RCMP watchdog were among the more than 20 prominent signatories to a letter calling for increased oversight of national spies. “Increased accountability has to come with increased powers for security forces,” the letter read.

National Defence Minister Jason Kenney has said the country maintains the “same strong” oversight as always, but critics point out the oversight regime was drafted during a different era of spying.

“I’m worried about the bill, not least because there appears to be a determination to rush it through Parliament,” said Joe Clark, former Progressive Conservative prime minister. “I don’t have the impression the government is prepared to consider amendments … I think that is unfortunate in any case, but it’s particularly dangerous in a case like this.”

What’s special about this case, Clark said, is this bill runs the risk of increasing the likelihood of dangers for Canadians at home.